1. Field of the Invention
The present invention relates to a communication terminal connected to a public line network, for sending and receiving short message data to/from another communication terminal via a center apparatus connected to the public line network.
2. Description of the Related Art
In recent years, a short message service system is constructed in which a short message service center (hereinafter, abbreviated as “SMSC”) apparatus connected to a public line network via a gateway or the like transmits short messages between communication terminals connected to the public line network by “store-and-forward”, which is a form of storage and forwarding of messages, utilizing wired or wireless communications, and a large number of communication terminal users utilize this system. The “short message” refers to character data constituted by not more than a predetermined number of characters such as about several tens of characters.
The short messages can be sent and received by the following two steps: the first step of storing (accumulating) short messages and the second step of forwarding (transferring) the short messages.
In the storing step, a short message is sent from a sending communication terminal to an SMSC apparatus, and the SMSC apparatus stores the received short message. In the forwarding step, the SMSC apparatus sends the received short message to a receiving-communication terminal.
In the storing step, the sending communication terminal dials the telephone number of the SMSC apparatus on a public line network in order to establish connection to the SMSC apparatus to send a short message to the SMSC apparatus. The switchboard of the public line network sends the ID (i.e., the telephone number) of the sender of the sending communication terminal in accordance with the incoming call signal (ringer). The SMSC apparatus uses the sender ID to identify the sending communication terminal and also uses the sender ID to charge the service fees after the identification. When a link of the communication line is established between the sending communication terminal and the SMSC apparatus, a phase of a short message transfer between the sending communication terminal and the SMSC apparatus is started. When the transfer of the short message from the sending communication terminal ends, the line is opened. The SMSC apparatus stores the short message received from the sending communication terminal in storing means.
In the forwarding step, the SMSC apparatus dials the telephone number of a receiving communication terminal on the public line network in order to establish connection to the receiving communication terminal to send the stored short message to the SMS compatible receiving communication terminal. The ID (telephone number) of the receiving communication terminal is contained in the short message in advance. The switchboard of the public line network sends the sender ID of the SMSC apparatus to the receiving communication terminal in accordance with the incoming call signal. The receiving communication terminal uses the sender ID of the SMSC apparatus to identify the sending apparatus. When the result of the identification confirmed that the incoming call is from the SMSC apparatus, the receiving communication terminal is switched automatically to the mode of receiving a short message and establishes a communication line with the SMSC apparatus, and when the line is established, the short message is transferred from the SMSC apparatus. When the transfer ends, the line is opened.
The short message transmission service (SMS) is performed by the above-described steps, and a large number of communication terminal users contract with an SMS provider for subscription and thus gain benefits.
Conventionally, a communication terminal user generally contracts with only one short message service provider, and therefore the short message service-compatible communication terminal receives and sends short messages only via the SMSC apparatus of the provider with whom the user contracted. Therefore, the user cannot use an SMSC apparatus other than that of the provider with whom the user contracted. Consequently, short messages cannot be sent and received to/from a user that uses a short message transmission service provided by the other providers. Furthermore, the billing terms of charges or the service available time zone depend on the provider, but the user cannot use other SMSC apparatuses than that of the provider with whom the user contracted. Therefore, there is no degree of freedom in the use conditions, and the convenience and the cost are problematic.